Various high temperature electric melting furnaces with differently configured electrodes have been devised for melting glass and refractory materials. In U.S. Pat. No. 3,983,309 to Faulkner et al., a melting furnace is disclosed which includes three rectangular or plate block electrodes inserted into the furnace from above. The outlet of the furnace includes an electrically conducting member. The three plate electrodes are spaced radially from the electrically conducting outlet member. The electrodes are laterally adjustable for altering melting conditions. In U.S. Pat. No. 3,539,691 to Lucek, a forehearth is described having two electrodes for overhead entry into melted material. The electrodes provide supplemental heat to maintain the material in a melted condition. The forehearth has a top covering or cap to prevent the escape of heat. In U.S. Pat. No. 2,686,821 to McMullen, a furnace is provided having a forehearth. Cylindrical carbon electrodes are mounted for positioning through the open top furnace. The position of the electrodes is vertically adjustable. In U.S. Pat. No. 2,089,690 to Cornelius, an electric furnace is illustrated wherein round tip electrodes are positioned into the furnace through the side walls thereof. In U.S. Pat. No. 2,591,709 to Lubatti, an electrode is shown including a lining or covering which surrounds a portion of the cylindrical shaft of the electrode.
Although numerous and diverse furnaces are shown in the prior art, none of these prior art furnaces have incorporated the structure of the present invention for optimizing both the melting and mixing of a non-homogeneous material prior to its discharge from a furnace outlet. The present invention incorporates electrodes having substantially round electrode tips which are insertable through the top of an opened furnace vessel having a bottom discharge outlet. Critical to efficient melting and mixing of the material in the furnace vessel is the spacing between each of the electrode tips and the depth thereof in the molten material.
As evidenced by U.S. Pat. No. 3,983,309 to Faulkner et al., laterally adjustable electrodes positioned through the top of the furnace are known. But, these electrodes have rectangular plate electrode tips positioned radially outwardly from the furnace outlet in the same plane thereof. When rectangular plate electrodes with an electrically conducting outlet are used as in the electric furnace of Faulkner et al., radial heat flow patterns are produced. The radial heat flow produced by electric current through the electrodes is in a direction away from the center of the furnace towards the side walls of the furnace. As a result, significant amounts of heat are lost to the furnace side walls, rather than being used to melt the material in the furnace. In contrast, the round or circular electrode tips of the present invention create circular flow patterns which results in the heat being maintained in the center of the furnace. As a consequence, rapid heat absorption by batch overlying the melted material is achieved in the furnace. Additionally, the circular flow patterns enhance mixing or agitation of the molten material so that a homogeneous material is discharged from the furnace vessel.
Even more significant, unlike the furnace of U.S. Pat. No. 3,983,309, the electrodes of this invention are spaced from each other and immersed a vertical distance in the molten material based upon defined furnace conditions, including the size of the furnace vessel, the magnitude of power applied to the furnace, and the temperature of the molten material in the furnace.
U.S. Pat. No. 3,539,691 to Lucek does show at least one round electrode tip in a two electrode furnace configuration. However, the Lucek electrodes are used in a forehearth, and not an electric melting furnace. The forehearth includes a cover so that the molten material is not open to the environment. A forehearth having a top closed to the surrounding environment is essential to prevent the unwanted escape of heat from the fully melted material before it exits the discharge outlet. In addition, forehearth electrodes are used to maintain the molten condition of the material contained therein. There is no additional melting or mixing thereof in the forehearth, unlike the present invention wherein optimum mixing of the molten material is a salient feature.